1. Field of the Invention
This invention relates to a disk storage apparatus, and is particularly concerned with a feature for controlling the velocity of a head during a seek operation.
2. Description of the Related Art
During a seek operation, a laser beam moves in the radiaI direction of a disk while crossing tracks. The velocity of the laser beam during the seek operation is detected based on a tracking error signal (TES) that indicates a deviation of the beam from the track center. The laser beam velocity control is usually performed so that the beam can be moved at an ideal velocity according to a distance to a target position.
In such velocity control, velocity information obtained from differentiating a TES is compared to a velocity profile that indicates an ideal velocity according to a distance to a target position. The velocity of a laser beam may be controlled so that a difference as the result of the comparison becomes zero. The velocity profile has a structure in which the beam reaches a target position in a short time and decelerates so as to surely shift to a track following operation at the target position. FIG. 3 provides an example indicating the relationship between a distance from a current position to a target position and a target velocity.
However, if the velocity information is obtained from the average of the amplitude of a signal obtained from differentiating the TES, the value of the velocity information shows a variation due to a shape of a track guide groove on the optical disk as well as scatter in circuit constants. Moreover, even if the velocity information is obtained independently of the differentiation of the TES, the value of the velocity information changes due to scatter in circuit constants. Accordingly, even if the velocity of the beam is controlled so that a difference between a detected velocity and an ideal velocity from the velocity profile becomes zero, the velocity at which the beam moves may be higher or lower than the ideal velocity as the case may be.
FIG. 7 shows values of detected velocity for values from the velocity profile, and the actual velocity at which the beam moves in a case where even if the velocity is controlled so that a difference between the detected velocity and the ideal velocity from the velocity profile becomes zero, the actual velocity of the movement of the beam becomes higher than the ideal velocity assumed theoretically. In this case, as is obvious from the FIG. 7, even if the beam reaches a target position, the beam is not satisfactorily decelerated. Thus the beam cannot shift to a track following operation at the target position.
FIG. 8 shows values of detected velocity for values from the velocity profile, and the actual velocity at which the beam moves in a case where even if the velocity is controlled so that a difference between the detected velocity and the ideal velocity from the velocity profile becomes zero, the actual velocity of the movement of the beam becomes lower than the ideal velocity assumed theoretically. In this case, as is obvious from FIG. 8, the velocity of the movement of the beam from the optical head becomes zero before a target track position is reached and thus that target track cannot be reached during one seek operation.
Further, even if the velocity information itself precisely shows an actual velocity, a driving signal generated based on the precise velocity information may fluctuate due to a large variety of circuit constants and cause a similar problem. Such a problem may be caused not only in an optical disk drive apparatus but in a magnetic disk drive apparatus.